Apparatus and methods including source gates

ABSTRACT

Apparatus and methods are disclosed, such as an apparatus that includes a string of charge storage devices associated with a pillar (e.g., of semiconductor material), a source gate device, and a source select device coupled between the source gate device and the string. Additional apparatus and methods are described.

PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No.14/451,145, filed Aug. 4, 2014, now issued as U.S. Pat. No. 9,378,839,which is a continuation of U.S. application Ser. No. 13/210,194, filedAug. 15, 2011, now issued as U.S. Pat. No. 8,797,806, all of which areincorporated herein by reference in their entirety.

BACKGROUND

Semiconductor memory devices are used in many electronic devices such aspersonal digital assistants (PDAs), laptop computers, mobile phones anddigital cameras. Some of these semiconductor memory devices have arraysof charge storage transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments are illustrated by way of example and not limitation inthe figures of the accompanying drawings in which:

FIGS. 1A and 1B are electrical schematic diagrams of a block of memorycells according to various embodiments of the invention;

FIG. 2 is a top view of a semiconductor construction according tovarious embodiments of the invention;

FIG. 3 is a cross-sectional view of a semiconductor constructionaccording to various embodiments of the invention;

FIG. 4 is a cross-sectional view of a semiconductor constructionaccording to various embodiments of the invention;

FIG. 5 is a top view of a semiconductor construction according tovarious embodiments of the invention;

FIG. 6 is a cross-sectional view of a semiconductor constructionaccording to various embodiments of the invention;

FIG. 7 is a cross-sectional view of a semiconductor constructionaccording to various embodiments of the invention;

FIG. 8 is a cross-sectional view of a semiconductor constructionaccording to various embodiments of the invention;

FIG. 9 is a flow diagram of a method according to various embodiments ofthe invention; and

FIG. 10 is a diagram illustrating a system according to variousembodiments of the invention.

DETAILED DESCRIPTION

An array of charge storage devices according to various embodiments ofthe invention may function as an array of memory cells in a memorydevice such as a NOT AND (NAND) memory device.

For the purposes of this document, a “tier of semiconductor material”can mean semiconductor material formed in a same plane, rank, row, orunit, such as in a horizontal or vertical or sloped plane, row, rank orunit of a structure. Meanwhile, an “apparatus” can refer to circuitry,devices or systems.

FIGS. 1A and 1B are electrical schematic diagrams of a block 100 ofmemory cells according to various embodiments of the invention. Theblock 100 includes strings 110 of charge storage devices 118. A singleNAND memory device may include multiple strings.

The strings 110 are arranged in rows and columns in the block 100. FIG.1A shows a single row of four strings 110 aligned with one verticalplane of the block 100 of memory cells. FIG. 1B shows three rows eachhaving four strings 110 (for a total of twelve strings 110). Each string110 includes four charge storage devices 118 coupled serially, althougheach string 110 may include fewer or more charge storage devices 118.Each string 110 includes a source select device 122 at a bottom of thestring 110 and a drain select device 126 at a top of the string 110.

The drain select device 126 is coupled between the charge storagedevices 118 and a data line 130. There are four data lines 130 that arecoupled to the strings 110, each data line 130 being coupled to three ofthe strings 110 in a column of the block 100. The source select device122 is coupled between the charge storage devices 118 and a source gate140.

The source select device 122 has a source select gate (SGS) coupled to aSGS line 150. There are three SGS lines 150 that are coupled to thesource select devices 122 in the block 100, each SGS line 150 beingcoupled to gates of four of the source select devices 122 in a row ofthe block 100. The SGS lines 150 are substantially orthogonal to thedata lines 130.

The drain select device 126 has a drain select gate (SGD) coupled to aSGD line 160. There are three SGD lines 160 that are coupled to thedrain select devices 126 in the block 100, each SGD line 160 beingcoupled to gates of four of the drain select devices 126 in a row of theblock 100. The SGD lines 160 are substantially orthogonal to the datalines 130. The source gate 140 substantially controls conduction in afirst channel in the string 110 represented by a first source gatedevice 170 and a second channel in a substrate (not shown) representedby a second source gate device 172. The source gates 140 of all of thestrings 110 in the block 100 are coupled to a single source gate line176. The second source gate devices 172 in each row of the block 100 arecoupled in series between the respective strings 110 and a common sourceline 180.

Each of the charge storage devices 118 may comprise a transistor havinga charge trap or a floating gate, for example. Each charge storagedevice 118 may comprise a multi-state device capable of holding multipleseparate and distinct threshold voltage states (e.g., corresponding torespective ranges of threshold voltages), each threshold voltage staterepresenting different data. Each of the source select device 122 andthe drain select device 126 may comprise a transistor.

FIG. 2 is a top view of a semiconductor construction 200 according tovarious embodiments of the invention. The semiconductor construction 200includes three-hundred and sixty pillars 204 comprising a semiconductormaterial. For example, the pillars 204 may comprise polysilicon. Each ofthe pillars 204 provides a channel for multiple charge storage devicesin a string in a NAND memory device.

The pillars 204 are arranged into eight rows of forty five columns witheach pillar 204 occupying an intersection of a row and a column. Thepillars 204 are divided into five blocks 210, 212, 214, 216 and 218separated from each other by either empty space 220 or a conductivemember (e.g., a conductive slot) 224 coupled to an n+ type diffusionregion 228. The empty space 220 and space around the members 224 arefilled with a dielectric (not shown) such as, for example, silicondioxide (SiO₂). Each of the blocks 210, 212, 214, 216 and 218 includesseventy two of the pillars 204 in eight rows of nine columns. Thepillars 204 in each row across all of the blocks 210, 212, 214, 216 and218 are coupled together by a data line 232 or 233 that may be used tosense a state of one of the charge storage devices in the row. The datalines 232 and 233 may comprise, for example, polysilicon or metal,including one or more of cobalt (Co), titanium (Ti), tungsten (W),nickel (Ni) or tantalum (Ta) according to various embodiments of theinvention. The semiconductor construction 200 can include differentnumbers of pillars 204 arranged in different numbers of rows and columnsin different numbers of blocks according to various embodiments of theinvention.

FIG. 3 is a cross-sectional view of the semiconductor construction 200along line 3-3 according to various embodiments of the invention andFIG. 4 is a cross-sectional view of the semiconductor construction 200along line 4-4 according to various embodiments of the invention. FIG. 3illustrates the pillars 204 in blocks 210 and 212 and one of the members224 between the blocks 210 and 212. FIG. 4 illustrates the pillars 204in the block 216.

The pillars 204 extend from the data lines 232 and 233 to a p-typesilicon well 310. The silicon well 310 is formed in an n-type siliconwell 312 which is formed in a p-type silicon substrate 316. The n+ typediffusion region 228 is formed in the silicon well 310 and can reduceresistance to current flow in the silicon well 310. A number of tiers ofmetal or semiconductor material surround or partially surround thepillars 204 between the data lines 232 and 233 and the silicon well 310in each of the blocks 210, 212, 214, 216 and 218. The tiers areseparated from each other by a dielectric (not shown) such as, forexample, silicon dioxide (SiO₂). A majority of the tiers are accesslines 320 and 322 to control the charge storage devices that receive andrelease charge through the pillars 204. Each of the access lines 320 and322 surrounds or partially surrounds all of the pillars 204 in a blocksuch as the blocks 210 and 212 shown in FIG. 3.

A tier between the access lines 320 and 322 and the data lines 232 and233 is divided into drain select gates (SGDs) 330 and 360 that maysubstantially control conduction between the pillars 204 and the datalines 232 and 233. The eight pillars 204 in each column are surroundedor partially surrounded by a separate SGD 330 or 360. A tier below theaccess lines 320 and 322 is divided into source select gates (SGSs) 340and 370 that may at least partially control conduction between thepillars 204 and the silicon well 310. The eight pillars 204 in eachcolumn are surrounded or partially surrounded by a separate SGS 340 or370.

A tier between the SGSs 340 and 370 and the silicon well 310 comprises asource gate 350. In the embodiment depicted in FIGS. 2-4, source gate350 surrounds or partially surrounds all of the pillars 204 in a blocksuch as the block 210 or the block 212 shown in FIG. 3. The source gate350 may at least partially control conduction between the pillars 204and the silicon well 310.

The members 224 each comprise a conductive structure, such as one havinga wall shape, coupled to the n+ type diffusion region 228 in the siliconwell 310, and that projects from the substrate 316. The members 224comprise, for example, a semiconductor such as polysilicon or a metalsuch as tungsten. Each member 224 and the n+ type diffusion region 228coupled to the member 224 can be used as a common source line in thesemiconductor construction 200. The members 224 can be used to bias thesilicon well 310 to a potential as desired. The members 224 can alsoreduce the resistance to current flow in the silicon well 310.

The access lines 320 and 322, the SGDs 330 and 360, the SGSs 340 and 370and the source gate 350 can be separated from each other by a dielectricsuch as, for example, silicon dioxide (SiO₂). The access lines 320 and322, the SGDs 330 and 360, the SGSs 340 and 370 and the source gate 350may comprise tiers of a semiconductor material such as silicon orpolysilicon or polysilicon doped with Phosphorous or Boron. The accesslines 320 and 322, the SGDs 330 and 360, the SGSs 340 and 370 and thesource gate 350 may also comprise metal including one or more of Cobalt(Co), Titanium (Ti), Tungsten (W), Nickel (Ni) or Tantalum (Ta)according to various embodiments of the invention.

The access lines 320 and 322 control charge storage devices surroundingor partially surrounding each pillar 204. Each charge storage device maycomprise, for example, a floating gate transistor or a charge traptransistor. The SGDs 330 and 360, the SGSs 340 and 370 and the sourcegate 350 control transistors surrounding or partially surrounding eachpillar 204.

Operations involving charge storage devices in the semiconductorconstruction 200 will be described with reference to a selected chargestorage device having a channel in a selected pillar 204 between the SGD360 and the SGS 370 in the block 212. The selected pillar 204 is coupledto the data line 233. The selected charge storage device is controlledby the access line 322.

The selected charge storage device is read when the voltages shown inTable 1 are applied to the semiconductor construction 200.

TABLE 1 Block 212 Block 210 Data line 233 ~0.3 V ~0.3 V   Data lines 232~0 V ~0 V Access line 322 0 to ~3 V ~0 V Access lines 320 ~6 V ~0 V SGD360 ~4 V N/A SGDs 330 ~0 V ~0 V SGS 370 ~4 V N/A SGSs 340 ~0 V ~0 VSource gate 350 ~5 V ~0 V Member 224 ~0 V ~0 V Silicon Well 310 ~0 V ~0V

Approximately 4 volts is applied to turn on the SGD 360 and the SGS 370and approximately 5 volts is applied to turn on the source gate 350 inthe block 212 to couple the selected pillar 204 to the data line 233 andthe silicon well 310. A channel develops in the silicon well 310 underthe block 212 due to the potential of the source gate 350 to carrycharge from the block 212 to the member 224 and the n+ type diffusionregion 228 coupled to the member 224 that can be a common source line.The access line 322 in the block 212 is coupled to between approximately0 volts and approximately 3 volts in stages to gradually turn on theselected charge storage device, which can be in one of a plurality ofcharge storage states. Approximately 6 volts are applied to the otheraccess lines 320 in the block 212 to render the other charge storagedevices associated with the selected pillar 204 conductive. The otherSGDs 330 and SGSs 340 in the block 212 are coupled to approximately 0volts and are not conductive, such that the channel does not receivecharge from the pillars 204 other than the selected pillar 204. The dataline 233 is precharged to approximately 0.3 volts to allow the selectedcharge storage device to be read, and the other data lines 232 are atapproximately 0 volts. The access lines 320, the SGDs 330, the SGSs 340and the source gate 350 in the block 210 are at approximately 0 volts.The data lines 232 and 233 and the silicon well 310 are at the samepotential for the blocks 210 and 212.

Charge storage devices associated with pillars other than the selectedpillar 204 can be influenced during a read by the access lines 320 atapproximately 6 volts, and may be programmed unintentionally. Thisunintentional programming is called read disturb. The inventors havediscovered that the challenge noted above, as well as others, can beaddressed by turning on the source gate 350 at 5 volts to allow the SGSs340 of the pillars other than the selected pillar 204 to be turned offto substantially electrically isolate the pillars other than theselected pillar 204 from the silicon well 310. The SGSs 340 that are notconductive substantially prevent conduction between the pillars otherthan the selected pillar 204 and the silicon well 310 to substantiallyprevent read disturb activity with respect to those pillars 204.

The selected charge storage device is programmed when the voltages shownin Table 2 are applied to the semiconductor construction 200.

TABLE 2 Block 212 Block 210 Data line 233 0 to ~1 V 0 to ~1 V Data lines232 ~2.3 V ~2.3 V Access line 322 ~20 V ~0 V Access lines 320 ~10 V ~0 VSGD 360 ~3 V N/A SGDs 330 ~0 V ~0 V SGS 370 0 to ~3 V N/A SGSs 340 0 to~3 V ~0 V Source gate 350 ~0 V ~0 V Member 224 0 to ~2 V 0 to ~2 VSilicon Well 310 ~0 V ~0 V

Approximately 3 volts is applied to turn on the SGD 360. The SGSs 340and 370 in the block 212 are biased to between approximately 0 andapproximately 3 volts and the member 224 is biased to betweenapproximately 0 and approximately 2 volts. The SGDs 330 and the sourcegate 350 in the block 212 and the silicon well 310 are biased toapproximately 0 volts. Approximately 20 volts are applied to the accessline 322 in the block 212 to turn on the selected charge storage deviceto program it. Approximately 10 volts are applied to the other accesslines 320 in the block 212 to render the other charge storage devicesassociated with the selected pillar 204 conductive. The SGDs 330 thatare biased to approximately 0 volts are not conductive such that thepillars in the block 212 other than the selected pillar 204 are floatingand have a potential that rises to approximately 8 volts due to thepotential on the access lines 320 of approximately 10 volts tosubstantially prevent programming. The data line 233 coupled to theselected pillar 204 is between approximately 0 and approximately 1 voltto allow the selected charge storage device to be programmed and theother data lines 232 are biased to approximately 2.3 volts. The accesslines 320, the SGDs 330, the SGSs 340 and the source gate 350 in theblock 210 are at approximately 0 volts. The data lines 232 and 233 andthe silicon well 310 are at the same potential for the blocks 210 and212.

The source gate 350 is switched off to substantially reduce leakage ofcurrent to the n+ type diffusion region 228 and the member 224 and thiscan reduce program disturb activity during programming operations. Thevoltage applied to the SGSs 340 and 370 can be higher than theapproximately 3 volts to reduce an electromagnetic field between theSGSs 340 and 370 and the access lines 320 and 322.

The selected charge storage device is erased when the voltages shown inTable 3 are applied to the semiconductor construction 200.

TABLE 3 Block 212 Block 210 Data lines 232, 233 ~20 V ~20 V Access lines320, 322  ~0 V ~20 V SGDs 330, 360 ~20 V ~20 V SGSs 340, 370 ~20 V ~20 VSource gate 350 ~20 V ~20 V Member 224 ~20 V ~20 V Silicon Well 310 ~20V ~20 V

Approximately 20 volts is applied to the silicon well 310 such that thepotential on the pillars 204 rises to approximately 20 volts. The SGSs340 and 370, the member 224, the source gate 350, the SGDs 330 and 360and the data lines 232 and 233 are left floating and rise toapproximately 20 volts from capacitive coupling with the pillars 204.Approximately 0 volts are applied to the access lines 320 and 322 in theblock 212 to erase the charge storage devices associated with the pillar204 above the SGS 370. The access lines 320 in the block 210 are alsoleft floating and rise to approximately 20 volts from capacitivecoupling with the pillars 204.

FIG. 5 is a top view of a semiconductor construction 500 according tovarious embodiments of the invention. The semiconductor construction 500includes two-hundred and fifty-six pillars 504 comprising asemiconductor material. For example, the pillars 504 may comprisepolysilicon. Each of the pillars 504 provides a channel for multiplecharge storage devices in a string in a NAND memory device.

The pillars 504 are divided into four blocks 510, 512, 514 and 516separated from each other by a conductive member 524 coupled to an n+type diffusion region 528. Each of the blocks 510, 512, 514 and 516includes 64 of the pillars 504 separated into sub-blocks 529, eachsub-block 529 including 16 of the pillars 504. Each sub-block 529 isseparated from neighboring sub-blocks 529 in the same block by an n+type diffusion region 530. Sixteen data lines 532 and 533 are coupled totops of the pillars 504, and the pillars 504 are arranged in twostaggered columns in each sub-block 529. The columns of the pillars 504are substantially perpendicular to the data lines 532 and 533 such thateach data line 532 and 533 is coupled to a top of only one of thepillars 504 in each sub-block 529 of the semiconductor construction 500.Each data line 532 and 533 may be used to sense a state of one of thecharge storage devices in one of the sub-blocks 529. The data lines 532and 533 may comprise, for example, polysilicon or metal, including oneor more of cobalt (Co), titanium (Ti), tungsten (W), nickel (Ni) ortantalum (Ta), according to various embodiments of the invention.

FIG. 6 is a cross-sectional view of the semiconductor construction 500along line 6-6 according to various embodiments of the invention andFIG. 7 is a cross-sectional view of the semiconductor construction 500along line 7-7 according to various embodiments of the invention. FIG. 6shows the pillars 504 in the blocks 510 and 512 and one of the members524 between the blocks 510 and 512. Half of the pillars 504 in theblocks 510 and 512 are shown in cross-section and half of the pillars504 in the blocks 510 and 512 are not shown in cross-section but arestaggered and behind the pillars 504 shown in cross-section. The pillars504 that are staggered and behind the pillars 504 shown in cross-sectionare coupled to a data line 532 behind the data line 533 shown in FIG. 6.FIG. 7 shows eight of the pillars 504 and half of the data lines 532 and533 in block 514 for purposes of brevity and clarity.

The pillars 504 extend from the data lines 532 and 533 to a p-typesilicon well 610. The silicon well 610 is formed in an n-type siliconwell 612 which is formed in a p-type silicon substrate 616. The n+ typediffusion regions 528 and 530 are formed in the silicon well 610 and canreduce resistance to current flow in the silicon well 610. A number oftiers of metal or semiconductor material surround or partially surroundthe pillars 504 between the data lines 532 and 533 and the silicon well610 in each of the blocks 510, 512, 514 and 516. The tiers are separatedfrom each other by a dielectric (not shown) such as, for example,silicon dioxide (SiO₂). A majority of the tiers comprise access lines620 and 622 to control the charge storage devices that receive andrelease charge through the pillars 504. All of the pillars 504 in asub-block 529 are surrounded or partially surrounded by respectiveaccess lines 620 or 622.

A tier between the access lines 620 and 622 and the data lines 532 and533 is divided into SGDs 630 and 660 that may substantially controlconduction between the pillars 504 and the data lines 532 and 533. Thepillars 504 in each sub-block 529 are surrounded or partially surroundedby a separate SGD 630 or 660. A tier below the access lines 620 and 622is divided into SGSs 640 and 670 that may at least partially controlconduction between the pillars 504 and the silicon well 610. The pillars504 in each sub-block 529 are surrounded or partially surrounded by aseparate SGS 640 or 670. A tier between the SGSs 640 and 670 and thesilicon well 610 is a source gate 650. The pillars 504 in each sub-block529 are surrounded or partially surrounded by a separate source gate650. The source gates 650 may also at least partially control conductionbetween the pillars 504 and the silicon well 610.

The members 524 each comprise a conductive structure, such as one havinga wall shape, coupled to the n+ type diffusion region 528 in the siliconwell 610, and that projects from the substrate 616. The members 524comprise, for example, a semiconductor such as polysilicon or a metalsuch as tungsten. Each member 524 and the n+ type diffusion region 528coupled to the member 524 can be used as a common source line in thesemiconductor construction 500. The members 524 can be used to bias thesilicon well 610 to a potential as desired. The members 524 can alsoreduce the resistance to current flow in the silicon well 610.

The access lines 620 and 622, the SGDs 630 and 660, the SGSs 640 and 670and the source gate 650 can be separated from each other by a dielectricsuch as, for example, silicon dioxide (SiO₂). The access lines 620 and622, the SGDs 630 and 660, the SGSs 640 and 670 and the source gate 650may comprise tiers of a semiconductor material such as silicon orpolysilicon or polysilicon doped with Phosphorous or Boron. The accesslines 620 and 622, the SGDs 630 and 660, the SGSs 640 and 670 and thesource gate 650 may also comprise metal including one or more of cobalt(Co), titanium (Ti), tungsten (W), nickel (Ni) or tantalum (Ta)according to various embodiments of the invention. The access lines 620and 622 control charge storage devices associated with each pillar 504.The SGDs 630 and 660, the SGSs 640 and 670 and the source gate 650control transistors surrounding or partially surrounding each pillar504. Each charge storage device may comprise, for example, a floatinggate transistor or a charge trap transistor.

Operations involving charge storage devices in the semiconductorconstruction 500 will be described with reference to a selected chargestorage device having a channel in a selected pillar 504 between the SGD660 and the SGS 670 in the block 512. The selected pillar 504 is coupledto the data line 533. The selected charge storage device is controlledby the access line 622.

The selected charge storage device is read when the voltages shown inTable 4 are applied to the semiconductor construction 500.

TABLE 4 Block 512 Block 510 Data line 533 ~0.3 V ~0.3 V   Data lines 532~0 V ~0 V Access line 622 0 to ~3 V ~0 V Access lines 620 ~6 V ~0 V SGD660 ~4 V ~0 V SGDs 630 ~0 V ~0 V SGS 670 ~4 V ~0 V SGSs 640 ~0 V ~0 VSource gate 650 ~5 V ~0 V Member 524 ~0 V ~0 V Silicon Well 610 ~0 V ~0V

Approximately 4 volts is applied to turn on the SGD 660 and the SGS 670and approximately 5 volts is applied to turn on the source gates 650 inthe block 512 to couple the selected pillar 504 to the data line 533 andthe silicon well 610. A channel develops in the silicon well 610 underthe block 512 due to the potential of the source gate 650 to carrycharge from the block 512 to the member 524 and the n+ type diffusionregion 528 coupled to the member 524 that can be a common source line.The access line 622 in the block 512 is biased to a potential fromapproximately 0 to approximately 3 volts in stages to gradually turn onthe selected charge storage device, which can be in one of a pluralityof charge storage states. Approximately 6 volts are applied to the otheraccess lines 620 in the block 512 and render the other charge storagedevices associated with the selected pillar 504 conductive. The otherSGDs 630 and SGSs 640 in the block 512 are biased to approximately 0volts and are not conductive such that the channel does not receivecharge from the pillars 504 other than the selected pillar 504. The dataline 533 is precharged to approximately 0.3 volts to allow the selectedcharge storage device to be read, and the other data lines 532 are atapproximately 0 volts. The access lines 620, the SGDs 630, the SGSs 640and the source gate 650 in the block 510 are at approximately 0 volts.The data lines 532 and 533 and the silicon well 610 are at the samepotential for the blocks 510 and 512. The pillar 504 that is between theSGD 660 and the SGS 670 that is not selected is not selected becauseit's coupled to one of the data lines 532 at approximately 0V.

The source gates 650 in the block 512 are turned on at 5 volts to allowthe SGSs 640 of the pillars other than the selected pillar 504 to beturned off to substantially electrically isolate the pillars other thanthe selected pillar 504 from the silicon well 610. The SGSs 640 that arenot conductive substantially prevent conduction between the pillarsother than the selected pillar 504 and the silicon well 610 tosubstantially prevent read disturb in those pillars.

The selected charge storage device is programmed when the voltages shownin Table 5 are applied to the semiconductor construction 500.

TABLE 5 Block 512 Block 510 Data line 533 0 to ~1 V 0 to ~1 V Data lines532 ~2.3 V ~2.3 V Access line 622 ~20 V ~0 V Access lines 620 ~10 V ~0 VSGD 660 ~3 V N/A SGDs 630 ~0 V ~0 V SGS 670 0 to ~3 V N/A SGSs 640 0 to~3 V ~0 V Source gate 650 ~0 V ~0 V Member 524 0 to ~2 V 0 to ~2 VSilicon Well 610 ~0 V ~0 V

Approximately 3 volts is applied to turn on the SGD 660 in the block512. The SGSs 640 and 670 in the block 512 are biased to betweenapproximately 0 and approximately 3 volts and the member 524 is biasedto between 0 and approximately 2 volts. The SGDs 630 and the source gate650 in the block 512 and the silicon well 610 are biased toapproximately 0 volts. Approximately 20 volts are applied to the accessline 622 in the block 512 to turn on the selected charge storage deviceto program it. Approximately 10 volts are applied to the other accesslines 620 in the block 512 and render the other charge storage devicesassociated with the selected pillar 504 conductive. The SGDs 630 in theblock 512 that are biased to approximately 0 volts are not conductive,such that the pillars other than the selected pillar 504 are floatingand have a potential that rises to approximately 8 volts due to thepotential on the access lines 620 of approximately 10 volts tosubstantially prevent programming. The data line 533 coupled to theselected pillar 504 is between approximately 0 volts and approximately 1volt to allow the selected charge storage device to be programmed andthe other data lines 532 are biased to approximately 2.3 volts. Theaccess lines 620, the SGDs 630, the SGSs 640 and the source gate 650 inthe block 510 are at approximately 0 volts. The data lines 532 and 533and the silicon well 610 are at the same potential for the blocks 510and 512.

The source gate 650 in the block 512 is switched off to substantiallyreduce leakage of current to the n+ type diffusion region 528 and themember 524 and this can reduce program disturb activity during theprogramming. The voltage applied to the SGSs 640 and 670 can be higherthan the approximately 3 volts, such as to reduce an electromagneticfield between the SGSs 640 and 670 and the access lines 620 and 622.

The selected charge storage device is erased when the voltages shown inTable 6 are applied to the semiconductor construction 500.

TABLE 6 Block 512 Block 510 Data lines 532, 533 ~20 V ~20 V Access lines620, 622  ~0 V ~20 V SGDs 630, 660 ~20 V ~20 V SGSs 640, 670 ~20 V ~20 VSource gate 650 ~20 V ~20 V Member 524 ~20 V ~20 V Silicon Well 610 ~20V ~20 V

Approximately 20 volts is applied to the silicon well 610 such that thepotential on the pillars 504 rises to approximately 20 volts. The SGSs640 and 670, the member 524, the source gate 650, the SGDs 630 and 660and the data lines 532 and 533 are left floating and rise toapproximately 20 volts from capacitive coupling with the pillars 504.Approximately 0 volts are applied to the access lines 620 and 622 in theblock 512 to erase the charge storage devices associated with the pillar504 above the SGS 670. The access lines 620 in the block 510 are leftfloating and rise to approximately 20 volts from capacitive couplingwith the pillars 504.

FIG. 8 is a cross-sectional view of the semiconductor construction 200along line 8-8 according to various embodiments of the invention. FIG. 8illustrates four of the pillars 204 in the block 218 extending from thedata line 233 to the p-type silicon well 310 and the tiers including theaccess lines 320 and 322, the SGDs 330, the SGSs 340 and the source gate350. Silicon dioxide 810 is formed at edges of the SGDs 330. FIG. 8illustrates charge storage devices 820 between the access lines 320 and322 and the pillars 204. Each charge storage device 820 includes apolysilicon storage layer 830 separated from one of the pillars 204 by atunnel dielectric 840 that can be silicon dioxide. The charge storagelayer 830 is separated from the access line 320 or 322 by a blockingdielectric 850 that can include silicon dioxide, silicon nitride (Si₃N₄)and silicon dioxide (ONO).

FIG. 9 is a flow diagram of a method 900 according to variousembodiments of the invention. In block 910, the method 900 starts. Inblock 920, strings are coupled to data lines. In block 930, the stringsare coupled to a substrate. In block 940, some of the strings aresubstantially electrically isolated from the substrate. In block 950,the method 900 ends. Various embodiments may have more or feweractivities than those shown in FIG. 9. In some embodiments, theactivities may be repeated, and/or performed in serial or parallelfashion. Some embodiments may comprise the same activities in adifferent order.

FIG. 10 is a diagram illustrating a system 1000 according to variousembodiments of the invention. The system 1000 may include a processor1010, a memory device 1020, a memory controller 1030, a graphiccontroller 1040, an input and output (I/O) controller 1050, a display1052, a keyboard 1054, a pointing device 1056, and a peripheral device1058. A bus 1060 couples all of these devices together. A clockgenerator 1070 is coupled to the bus 1060 to provide a clock signal toat least one of the devices of the system 1000 through the bus 1060. Theclock generator 1070 may include an oscillator in a circuit board suchas a motherboard. Two or more devices shown in system 1000 may be formedin a single integrated circuit chip. The memory device 1020 may compriseone or more of the block 100 of memory cells described herein and shownin the figures (e.g., see FIGS. 2A and 1B) according to variousembodiments of the invention.

The memory device 1020 may comprise one or more of the semiconductorconstructions 200, 500 and 800 described herein and shown in the figuresaccording to various embodiments of the invention. The bus 1060 may beinterconnect traces on a circuit board or may be one or more cables. Thebus 1060 may couple the devices of the system 1000 by wireless meanssuch as by electromagnetic radiations, for example, radio waves. Theperipheral device 1058 coupled to the I/O controller 1050 may be aprinter, an optical device such as a CD-ROM and a DVD reader and writer,a magnetic device reader and writer such as a floppy disk driver, or anaudio device such as a microphone.

The system 1000 represented by FIG. 10 may include computers (e.g.,desktops, laptops, hand-helds, servers, Web appliances, routers, etc.),wireless communication devices (e.g., cellular phones, cordless phones,pagers, personal digital assistants, etc.), computer-related peripherals(e.g., printers, scanners, monitors, etc.), entertainment devices (e.g.,televisions, radios, stereos, tape and compact disc players, videocassette recorders, camcorders, digital cameras, MP3 (Motion PictureExperts Group, Audio Layer 3) players, video games, watches, etc.), andthe like.

Charge storage devices in NAND memory devices can be subject to readdisturb stress during read operations. The inventors have discoveredthat the challenges noted above, as well as others, can be addressedwith, for example, a source gate device coupled to strings between oneor more source select devices and a well in a substrate. Read disturbstress can be substantially reduced by turning off the source selectdevices in deselected strings during a read operation to substantiallyelectrically isolate the deselected strings from the well in thesubstrate to substantially prevent conduction between the deselectedstrings and the well. A conductive member coupled to the substrate canreduce resistance to current flow in the well in the substrate.

Example structures and methods of fabricating semiconductor devices havebeen described. Although specific embodiments have been described, itwill be evident that various modifications and changes may be made tothese embodiments. Accordingly, the specification and drawings are to beregarded in an illustrative rather than a restrictive sense.

The Abstract of the Disclosure is provided to comply with 37 C.F.R.§1.72(b), requiring an abstract that allows the reader to quicklyascertain the nature of the technical disclosure. It is submitted withthe understanding that it will not be used to interpret or limit theclaims. In addition, in the foregoing Detailed Description, it may beseen that various features are grouped together in a single embodimentfor the purpose of streamlining the disclosure. This method ofdisclosure is not to be interpreted as limiting the claims. Thus, thefollowing claims are hereby incorporated into the Detailed Description,with each claim standing on its own as a separate embodiment.

What is claimed is:
 1. An apparatus comprising: a first string of chargestorage devices associated with a pillar comprising semiconductormaterial; a second string of charge storage devices associated with apillar comprising semiconductor material; a first source select devicehaving a gate, the first source select device coupled to the firststring of charge storage devices; a second source select device having agate, the second source select device coupled to the second string ofcharge storage devices, wherein the gates of the first and second sourceselect devices are separated from one another; a first source gatedevice having a gate, the first source gate device coupled between thefirst source select device and a source; and a second source gate devicehaving a gate, the second source gate device coupled between the secondsource select device and the source, wherein the gates of the first andsecond source gate devices are coupled to one another to be controlledin common.
 2. The apparatus of claim 1, comprising: a third string ofcharge storage devices associated with a pillar comprising semiconductormaterial; a fourth string of charge storage devices associated with apillar comprising semiconductor material; a third source select devicehaving a gate, the third source select device coupled to the thirdstring of charge storage devices; a fourth source select device having agate, the fourth source select device coupled to the fourth string ofcharge storage devices, wherein the gates of the third and fourth sourceselect devices are separated from each other; a third source gate devicehaving a gate, the third source gate device coupled between the thirdsource select device and the source; and a fourth source gate devicehaving a gate, the fourth source gate device coupled between the fourthsource select device and the source; and wherein the gates of the first,second, third, and fourth source gate devices are coupled to one anotherto be controlled in common.
 3. The apparatus of claim 2, wherein: gatesof the first and third source select devices are coupled to each otherto be controlled in common; and gates of the second and fourth sourceselect devices are coupled to each other to be controlled in common. 4.The apparatus of claim 3, further comprising: a first drain selectdevice having a gate, the first drain select device coupled to the firststring of charge storage device; a second drain select device having agate, the second drain select device coupled to the second string ofcharge storage devices; a third drain select device having a gate, thethird drain select device coupled to the third string of charge storagedevices; and a fourth drain select device having a gate, the fourthdrain select device coupled to the fourth string of charge storagedevices: wherein gates of the first and second drain select devices areseparated from each other, wherein gates of the first and third drainselect devices are coupled to each other to be controlled in common, andwherein gates of the second and fourth drain select devices are coupledto each other to be controlled in common.
 5. The apparatus of claim 1,wherein the first string of the charge storage devices comprises afloating gate transistor.
 6. The apparatus of claim 1, wherein thesecond string of the charge storage devices comprises a charge traptransistor.
 7. The apparatus of claim 1, wherein the pillar extends froma data line to a well in a substrate.
 8. The apparatus of claim 1,wherein a distance between two gates of the charge storage devicesassociated with a pillar is shorter than a distance between the gate ofthe first source select device and the gate of the first source gatedevice.
 9. The apparatus of claim 1, comprising: a first block of memorycells comprising, the first string of charge storage devices, the secondstring of charge storage devices, the first source select device, thesecond source select device, the first source gate device, and thesecond source gate device.
 10. The apparatus of claim 9, comprising: asecond block of memory cells, comprising, a third string of chargestorage devices associated with a pillar comprising semiconductormaterial; a fourth string of charge storage devices associated with apillar comprising semiconductor material; a third source select devicehaving a gate, the third source select device coupled to the thirdstring of charge storage devices; a fourth source select device having agate, the fourth source select device coupled to the fourth string ofcharge storage devices, wherein the gates of the third and fourth sourceselect devices are separated from the gates of the first and secondsource select devices; a third source gate device having a gate, thethird source gate device coupled between the third source select deviceand a second source; and a fourth source gate device having a gate, thefourth source gate device coupled between the fourth source selectdevice and the source, wherein the gates of the first, second, third andfourth source gate devices are coupled to each other to be controlled incommon.
 11. An apparatus, comprising: multiple strings comprising chargestorage devices; a first unit of source select devices respectivelycoupled to strings of a first group of strings of the multiple stringsto control conduction between the strings of the first group and asource; a second unit of source select devices respectively coupled tostrings of a second group of strings of the multiple strings to controlconduction between the strings of the second group and the source, thefirst group of strings being different from the second group of strings;and a first unit of source gate devices, each respectively coupled inseries with a source select device of the first and second units ofsource select devices, to control conduction between the strings of thefirst and second groups of strings and the source.
 12. The apparatus ofclaim 11, comprising a first unit of drain select devices, each coupledto a respective string of the first group of strings, to controlconduction between the string and a first data line region; and a secondunit of drain select devices, each coupled to a respective string of thesecond group of strings, to control conduction between the string and asecond data line region.
 13. The apparatus of claim 11, wherein thedevices of the third unit of source gate devices are coupled to stringsin a block.
 14. The apparatus of claim 13, wherein the first unit ofsource select devices is coupled to strings of a first sub-block and thesecond unit of source select devices is coupled to strings of a secondsub-block.
 15. The apparatus of claim 11, wherein a distance between twogates of charge storage devices associated with one string is shorterthan a distance between a gate of one source select device associatedwith the first unit of source select devices and a gate of one sourcegate device associated with the third unit of source gate devices. 16.The apparatus of claim 11, wherein the charge storage devices comprisefloating gate transistors.
 17. The apparatus of claim 11, wherein thecharge storage devices comprise charge trap transistors.
 18. Anapparatus comprising: a memory unit including: multiple strings ofcharge storage devices connected by a channel, strings arranged inmultiple rows, each string associated with a pillar comprisingsemiconductor material; and each string in a row including, a sourcegate device coupled to a source and configured to control conductionbetween the channel of charge storage devices in the string and thesource, wherein a gate of the source gate device is coupled to the gateof another source gate device in the same row of the multiple rows inthe memory unit, and also to the gate of a source gate device in anotherrow of the multiple rows in the memory unit; and a source select devicecoupled between the channel of charge storage devices and the sourcegate device, the source select device configured to control conductionbetween the channel and the source.
 19. The apparatus of claim 18,wherein the source select device has a gate, and wherein the gate of thesource select device is coupled to the gate of another source selectdevice of another string.
 20. The apparatus of claim 18, wherein thegates of all source gate devices in a memory block are coupled in commonwith one another.